System and Method for Channel State Information Feedback in Wireless Communications Systems

ABSTRACT

A system and method for channel state information feedback in wireless communications systems are provided. A method for reporting channel information includes determining, at a user equipment, a channel information type for first channel information to be reported to a communications controller, determining the first channel information conditioned on previously reported channel information and on the channel information type, and reporting the first channel information, the channel information type, or a combination thereof, to the communications controller.

This application claims the benefit of U.S. Provisional Application No.61/383,251, filed on Sep. 15, 2010, entitled “Method and Apparatus forCSI Feedback for Closed Loop MIMO Systems,” which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to digital communications, andmore particularly to a system and method for channel state informationfeedback in wireless communication systems.

BACKGROUND

In a wireless communications system, the communications system'scapacity may be significantly improved when a first device has full orpartial knowledge of a channel (e.g., channel information) over which itwill be transmitting. The channel information may be referred to aschannel state information (CSI). CSI may be obtained by the first deviceover a reverse feedback channel, where a second device that receivestransmissions made by the first device transmits CSI to the first deviceover the reverse feedback channel.

Generally, communications in a communications system occur overuni-directional links. A first uni-directional link may be referred toas a downlink (DL) that originates at a communications controller (alsocommonly referred to as a base station, a NodeB, an enhanced NodeB(eNB), and so on) and ends at a communications device (also commonlyreferred to as a mobile station, a terminal, a subscriber, a UserEquipment (UE), and so forth). A second uni-directional link may bereferred to as an uplink (UL) that originates at the communicationsdevice and terminates at the communications controller. In the DL, thecommunications controller may be the first device and the communicationsdevice may be the second device.

The capacity and coverage of the wireless communication system can besignificantly improved by using multiple antennas at transmitter and/orreceiver. Such wireless communications systems are referred to asMultiple Input Multiple Output (MIMO) systems and can exploit thespatial dimension of the communication channel to transmit severalparallel information carrying signals, commonly referred to as spatialmultiplexing. The additional gains can be achieved by adaptation of anumber of simultaneously transmitted information carrying signals to alevel that the channel can support, which is commonly referred to astransmission rank adaptation.

Additional gain can be also obtained by using precoding that adjusts thephase and amplitude of the signals to better fit current channelconditions. The aforementioned signals form a vector-valued signal andthe adjustment operation can be implemented as multiplication with aprecoding matrix. Based on information related to channel conditions,the precoding matrix can be chosen from a finite and countable set, aso-called codebook. A different codebook can be defined for differenttransmission rank and the precoding matrix can be indexed by a precodingmatrix indicator from the corresponding codebook.

SUMMARY OF THE INVENTION

These technical advantages are generally achieved, by exampleembodiments of the present invention which provide a system and methodfor channel state information feedback in wireless communicationssystems.

In accordance with an example embodiment of the present invention, amethod for reporting channel information is provided. The methodincludes determining, at a user equipment, a channel information typefor first channel information to be reported to a communicationscontroller, determining the first channel information conditioned onpreviously reported channel information and on the channel informationtype, and reporting the first channel information, the channelinformation type, or a combination thereof, to the communicationscontroller.

In accordance with another example embodiment of the present invention,a user equipment is provided. The user equipment includes a processor,and a transmitter coupled to the processor. The processor determines achannel information type for first channel information to be reported toa communications controller, and determines the first channelinformation conditioned on previously reported channel information andon the channel information type. The transmitter reports the firstchannel information, the channel information type, or a combinationthereof, to the communications controller.

In accordance with another example embodiment of the present invention,a communications system is provided. The communications system includesa communications controller, and a user equipment coupled to thecommunications controller. The communications controller controls userequipment. The user equipment determines a channel information type forfirst channel information to be reported to the communicationscontroller, determines the first channel information conditioned onpreviously reported channel information and on the channel informationtype, and reports the first channel information, the channel informationtype, or a combination thereof, to the communications controller.

One advantage disclosed herein is that for some types of feedbackinformation that a UE is incapable of computing may be determinedconditioned on (or based on) previously reported feedback information.The use of previously reported feedback information to condition thesetypes of feedback information yields better overall communicationssystem performance than using randomly selected or fixed information forthese types of feedback information.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the embodiments that follow may be better understood.Additional features and advantages of the embodiments will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 a illustrates an example portion of a wireless communicationssystem according to example embodiments described herein;

FIG. 1 b illustrates an example wireless communications system utilizinga codebook in communications channel information feedback according toexample embodiments described herein;

FIG. 2 a illustrates an example eNB according to example embodimentsdescribed herein;

FIG. 2 b illustrates an example UE according to example embodimentsdescribed herein;

FIG. 3 a illustrates an example diagram of a first CSI report sequenceas transmitted by a UE to an eNB with PTI=0 according to exampleembodiments described herein;

FIG. 3 b illustrates an example diagram of a second CSI report sequenceas transmitted by a UE to an eNB with PTI=1 according to exampleembodiments described herein;

FIG. 4 a illustrates an example first diagram of CSI feedbacktransmitted by a UE to an eNB, wherein one of the CSI is determinedconditioned on previously reported CSI according to example embodimentsdescribed herein;

FIG. 4 b illustrates an example second diagram of CSI feedbacktransmitted by a UE to an eNB, wherein one of the CSI is determinedconditioned on previously reported CSI according to example embodimentsdescribed herein;

FIG. 4 c illustrates an example third diagram of CSI feedbacktransmitted by a UE to an eNB, wherein one of the CSI is determinedconditioned on previously reported CSI according to example embodimentsdescribed herein;

FIG. 5 illustrates an example flow diagram of UE operations in reportingCSI to an eNB according to example embodiments described herein;

FIGS. 6 a through 6 c illustrate several example determining of CSIconditioned on previously reported CSI according to example embodimentsdescribed herein; and

FIG. 7 illustrates an example communications device according to exampleembodiments described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the current example embodiments are discussed indetail below. It should be appreciated, however, that the presentinvention provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

One exemplary embodiment of the invention relates to determining channelstate information (CSI) that is unavailable in a current operating modeor CSI report sequence by conditioning it on previously reported CSI.The UE may determine the CSI using the previously reported CSI andchannel information type to help formulate the CSI. For example, a UEthat provides CSI to an eNB may generate certain types of CSI that areunavailable in a current operating mode by using previously reported CSIand channel information type to help it generate the CSI that moreaccurately captures the channel state than a randomly selected CSI or afixed CSI value would be able to capture. The UE may then report the CSIand/or the channel information type.

The present invention will be described with respect to exampleembodiments in a specific context, namely a Third Generation PartnershipProject (3GPP) Long Term Evolution (LTE) Release-10 compliantcommunications system. The invention may also be applied, however, toother standards compliant and non-standards compliant communicationssystems that use dual index or double codebook based CSI feedback toimprove overall communications system performance.

FIG. 1 a illustrates a portion of a wireless communications system 100.Wireless communications system 100 includes an enhanced NodeB (eNB) 105and a User Equipment (UE) 110. Transmissions from eNB 105 to UE 110occur over channel 115. UE 110 estimates channel 115 and provideschannel information regarding channel 115 (such as CSI) to eNB 105. UE110 may utilize a feedback channel 117 to transmit the channelinformation regarding channel 115 to eNB 105.

While it is understood that communications systems may employ multipleeNBs capable of communicating with a number of UEs, only one eNB and oneUE are illustrated for simplicity.

eNB 105 includes a processor 120, a transmitter 125 with one or moretransmit antennas 126, and a receiver 130 with one or more receiveantenna 131. Similarly, UE 110 includes a processor 140, a receiver 145with one or more receive antenna 146, and a transmitter 150 with one ormore transmit antenna 151.

Receiver 145 of UE 110 receives transmissions made by transmitter 125 ofeNB 105 and from the received transmissions, processor 140 may computechannel information, such as channel mean, spatial domain channelcorrelation matrix, long and/or short term channel statistics, functionsthereof, and so forth. The channel information (in full or partial form)may be transmitted back to eNB 105, where it is received by receiver 130and provided to processor 120 that makes use of the channel informationto design future transmissions. The channel information may be quantizedto help reduce feedback overhead.

The channel information fed back to eNB 105 by UE 110 may be in the formof time domain channel information, frequency domain channelinformation, or a combination thereof. Time domain channel informationmay be in the form of short term channel information or long termchannel information, while frequency domain channel information may bein the form of sub-band channel information or wideband channelinformation. In general, long term channel information and/or widebandchannel information may be collectively referred to as “long term”and/or “wideband” channel statistics or “long term wideband” channelstatistics. Short term channel information may include channel mean, andso on.

FIG. 1 b illustrates a wireless communications system 150 utilizing acodebook in communications channel information feedback. Wirelesscommunications system 150 includes a eNB 155 transmitting to a UE 160over a channel 165. In order to improve performance, UE 160 measures andtransmits information related to channel 165 (i.e., channel information)to eNB 155. Since a feedback channel used to transmit the feedbackinformation may have limited resources, reducing feedback informationoverhead may help to improve overall communications system performance.

One technique commonly used to reduce feedback information overhead forsome forms of channel information is to use a codebook to quantize thechannel information and then feeding back only an index into thecodebook to eNB 155 instead of the actual channel information of channel165. Both UE 160 and eNB 155 possess copies of the codebook (shown ascodebook 170 for UE 160 and codebook 175 for eNB 155). The codebook usedfor quantizing the channel information of channel 165 may be predefinedand fixed.

FIG. 2 a illustrates an eNB 201. Data 200, in the form of bits, symbols,or packets for example, destined for a plurality of UEs being served aresent to a scheduler 204, which decides which UEs will be transmitted toin a given time and/or frequency opportunity. For example, withMulti-User Multiple Input Multiple Output (MU-MIMO), scheduler 204 mayselect L out of K UEs for transmission at a given time and frequencyresource, where K and L are integer values and L is less than or equalto K. The selection of the L UEs may be in accordance with factors suchas maximizing throughput, service history, UE priority, informationpriority, and so forth. While for Single User MIMO (SU-MIMO), scheduler204 may select single UEs for transmission at a given time and frequencyresource.

Data for UEs are processed by modulation and coding block 210 to convertto transmitted symbols and add redundancy for the purpose of assistingwith error correction or error detection. The modulation and codingscheme is chosen based in part on or in accordance with informationabout the channel information feedback 215.

The output of modulation and coding block 210 is passed to a transmitbeamforming block 220, which maps the coded and modulated stream foreach UE onto a beamforming vector. The beamformed outputs are coupled toantennas 216 through RF circuitry. The transmit beamforming vectors maybe determined by transmit beamforming block 220, which may determine thetransmit beamforming vectors in accordance with channel informationfeedback 215 as well as information from scheduler 204, which mayinclude information regarding the UEs selected for transmission, and soon.

Feedback processor 202, among other operations, decodes feedbackinformation from channel information feedback 215. Decoding feedbackinformation may involve the use of a codebook 205 if channel informationfeedback 215 was quantized using a codebook by a UE.

The channel information may be fed back with different periodicity. Asan example, Rank Indication (RI) may be fed back at a relatively longperiod, as is long term channel information, while wideband PrecodingMatrix Indicator (PMI) and/or Channel Quality Indicator (CQI); andsubband PMI and/or CQI (subband PMI/CQI) may be fed back at a relativelyshort period. Feedback processor 202 may need to process the receivedchannel information feedback 215 differently in accordance with the typeof channel information.

Additionally, channel information feedback 215 may be encoded to protectfrom transmission errors. The encoding may be jointly or separatelyperformed. If so protected, feedback processor 202 may remove theencoding used to protect channel information feedback 215 to producefeedback information.

Scheduler 204 may use any of the known scheduling disciplines in theliterature including round robin, maximum sum rate, proportional fair,minimum remaining processing time, or maximum weighted sum rate;generally scheduling decisions are in accordance with channelinformation feedback 215 received from the plurality of UEs. Scheduler204 may decide to send information to a single UE via transmitbeamforming (SU-MIMO) or may decide to serve multiple UEs simultaneouslythrough MU-MIMO communications.

Modulation and coding unit 210 may perform any number of coding andmodulation techniques including quadrature amplitude modulation, phaseshift keying, frequency shift keying, differential phase modulation,convolutional coding, turbo coding, bit interleaved convolutionalcoding, low density parity check coding, fountain coding, or blockcoding. The choice of modulation and coding rate in a preferredembodiment may be made in accordance with channel information feedback215 in a preferred embodiment and may be determined jointly in scheduler204.

While not explicitly illustrated, it is obvious to those of ordinaryskill in the art that OFDM modulation can be used. Further, any numberof multiple access techniques could be used including orthogonalfrequency division multiple access, code division multiple access,frequency division multiple access, or time division multiple access.The multiple access technique may be combined with the modulation andcoding unit 210 or the transmit beamforming block 220 among others.

Channel information feedback 215 may, for purposes of illustration, bein the form of quantized channel measurements, modulation, coding,and/or spatial formatting decisions, received signal strength, andsignal-to-interference-plus-noise measurements. A processor 235 may beused to execute applications for eNB 201, and may be used to control theoperation of units such as feedback processor 202, codebook adjust unit206, modulation and coding unit 210, scheduler 204, and so forth.

FIG. 2 b illustrates UE 203. UE 203 may have one or more receiveantennas 251, connecting through RF circuitry to a receiver signalprocessing unit 250. Receiver signal processing unit 250 includes achannel estimation unit 255.

Channel estimation unit 255 may employ any number of algorithms known inthe art including least squares, maximum likelihood, maximum a postiori,Bayesian estimator, adaptive estimator, a blind estimator, or so forth,to estimate a channel between UE 203 and its serving eNB. Somealgorithms exploit known information inserted into the transmit signalin the form of training signals, training pilots, while others usestructure in the transmitted signal such as cyclostationarity toestimate coefficients of the channel between the eNB and the UE.

Channel quality information unit 275 generates channel information basedon channel estimates from channel estimation unit 255 and potentiallypreviously reported channel information. Channel quality informationunit 275 may also make use of a codebook 280 to generate the channelinformation. Channel information may include rank indicator, precodingmatrix indicator, channel quality indicator, and so on. The channelinformation may be placed in a feedback message to produce channelinformation feedback 215. Channel quality information unit 275 may alsoapply an error correcting code to protect information in the feedbackmessage from errors.

The above codebook based precoding for closed loop MIMO is used in theThird Generation Partnership (3GPP) Long Term Evolution (LTE) Release-8system. The User Equipment (UE) would typically evaluate the differenttransmission rank and the precoding matrices in the codebook and reporta preferred rank indicator (RI) and a precoding matrix indicator (PMI)to its eNB. The eNB would then decide the transmission rank and theprecoding matrix, based on the received reports. Furthermore, ChannelQuality Indicator(s) (CQI) calculated conditioned on the use of theselected precoding matrix is (are) reported to eNB for link adaptation,scheduling and user pairing in MU-MIMO. Through feedback of the abovechannel state information (CSI) including RI, PMI, CQI, and so forth,the close loop MIMO system can adapt the transmission to the currentchannel conditions and hence achieve significant performance gain.

Periodic CSI report using a Physical Uplink Control Channel (PUCCH) andaperiodic CSI report using a Physical Uplink Shared Channel (PUSCH) forCQI, PMI, RI are defined and configured by higher layer signaling in 3GPLTE Release-8. Furthermore, the entire system bandwidth is partitionedinto multiple subbands. RI is usually determined assuming transmissionon system bandwidth. While CQI and PMI calculated assuming transmissionon system bandwidth is called wideband CQI and PMI. However, CQI and PMIcalculated assuming transmission on subband is called subband CQI andPMI.

A periodic CSI reporting mode defined in 3GPP LTE Release-8 is referredto as PUCCH mode 2-1 where RI, wideband CQI and wideband PMI, and UEselected subband CQI reports are respectively reported in differentsubframes. A UE selected subband CQI report in a certain subframedescribes the channel quality in a particular part or in particularparts of the bandwidth described subsequently as a bandwidth part (BP)or parts. A BP consists of multiple frequency-consecutive subbands andis indexed in the order of increasing frequency and non-increasing sizesstarting at the lowest frequency. Collectively, all of the BPs span theentire system bandwidth.

For UE selected subband CQI feedback, a single subband out of allsubbands of a BP is selected along with a corresponding label indexed inthe order of increasing frequency. The subband label will be reportedwith subband CQI report in the same subframe. The wideband CQI andwideband PMI report has period H·N_(pd). The integer H is defined asH=J·K+1, where J is the number of bandwidth parts. Between every twoconsecutive wideband CQI/wideband PMI reports, the remaining J·Kreporting instances are used in sequence for subband CQI reports on Kfull cycles of BPs. Each full cycle of BPs shall be in increasing orderstarting from BP 0 to BP J−1. The reporting interval of the RI reportingis an integer multiple M_(RI) of period H·N_(pd) (in subframes). Theparameter N_(pd) is the report period of subband CQI. Parameters K andM_(RI) are all configured using higher-layer signaling.

To improve granularity of spatial quantization without large overheadincrement, a double codebook or dual index based feedback framework wasadopted for 3GPP LTE Release-10 systems, where a precoder or a precodingmatrix W for a subband is a matrix product of two matrices W1 and W2.Matrix W1 targets long-term or wideband channel properties and matrix W2targets short-term or frequency-selective channel properties. W1 and W2are actually from two different codebooks C1 and C2, respectively. Forconvenience, hereinafter, the indices for W1 and W2 are referred to asfirst PMI and the second PMI, respectively. Equivalently, the first PMIand the second PMI can be said to index the matrix W, the matrix productof W1 and W2.

An extension of PUCCH Mode 2-1 in 3GPP LTE Release-8 was adopted in 3GPPLTE Release-10, which can be summarized as follows.

-   -   W is determined from 3-subframe report conditioned upon the        latest RI report.    -   Reporting format        -   Report 1: RI and 1-bit precoder type indication (PTI)        -   Report 2:            -   PTI=0: W1 will be reported;            -   PTI=1: wideband CQI and wideband W2 will be reported        -   Report 3:            -   PTI=0: wideband CQI and wideband W2 will be reported            -   PTI=1: subband CQI, subband W2, and a subband selection                indicator or predefined cycling.

As shown above, a new CSI port, PTI, is introduced, leading to twopossible CSI report sequences that are dependent on PTI value. A firstreport sequence comprises RI with PTI=0; W1 or first PMI; and widebandCQI, and wideband W2 or wideband second PMI. A second report sequencecomprises RI with PTI=1; wideband CQI, and wideband W2 or widebandsecond PMI; and subband CQI, and subbband W2 or subband second PMI.Furthermore, a subband selection indicator such as a subband labelwithin a bandwidth part (BP) can be reported with subband CQI andsubband second PMI. Alternatively, subband label or subband indicatorcan be obtained at the DE and the eNB from a predefined cycling patternknown for the UE and the eNB. Hereinafter, it is assumed that a subbandselection indicator or subband label can be reported with subband CQIand subband second PMI except that an explicit description about subbandselection indicator or subband label is specifically provided.

FIG. 3 a illustrates a diagram 300 of a first CSI report sequence astransmitted by a UE to an eNB with PTI=0, where a particular subframe isdepicted as a pulse. The first CSI report sequence fed back from a UE toan eNB with PTI=0 may begin with a RI with PTI=0 report (shown assubframe 305) followed by a number of W1 or wideband first PMI reports(shown as subframe 310, subframe 315, and subframe 320). In between thefeeding back of W1 or wideband first PMI reports, the UE may feedbackM−1 wideband CQI and W2 or wideband second PMI reports (shown as pulse312, pulse 314, and pulse 317), where M is a parameter that may besignaled to the UE through higher layer signaling, for example.

A time period between feedbacks of the M−1 wideband CQI and wideband W2or wideband second PMI reports may be defined as value P. Hence, aduration between consecutive feedbacks of W1 or wideband first PMIreports may be defined as M*P (or equivalently, H*P).

In summary, the first CSI report sequence may be defined as a sequenceof CSI reports beginning with a RI report with PTI=0 followed by anumber of W1 or wideband first PMI reports, with M−1 wideband CQI and W2or wideband second PMI reports in between adjacent W1 or wideband firstPMI reports.

FIG. 3 b illustrates a diagram 350 of a second CSI report sequence astransmitted by a UE to an eNB with PTI=1, where a particular subframe isdepicted as a pulse. The second CSI report sequence fed back from a UEto an eNB with PTI=1 may begin with a RI with PTI=1 report (shown assubframe 355) followed by a number of wideband CQI and wideband W2 orwideband second PMI reports (shown as pulse 360, pulse 365, and pulse370). In between the feeding back of wideband CQI and wideband W2 orwideband second PMI reports, the UE may feedback J*K subband CQI andsubband W2 or subband second PMI reports (shown as subframe 362,subframe 364, and subframe 367), where J is the number of BPs and K is aparameter that may be signaled to the UE through higher layer signaling,for example.

Again, a time period between feedbacks of the J*K subband CQI andsubband W2 or subband second PMI reports may be defined as value P.Hence, a duration between consecutive feedbacks of wideband CQI andwideband W2 or second PMI reports may be defined as (J*K+1)*P.

In summary, the second CSI report sequence may be defined as a sequenceof CSI reports beginning with a RI report with PTI=1 followed by anumber of wideband CQI and wideband W2 or wideband second PMI reports,with J*K subband CQI and subband W2 or subband second PMI reports inbetween adjacent wideband CQI and wideband W2 or wideband second PMIreports.

Although the CSI report sequences (e.g., the first CSI report sequenceand the second CSI report sequence) in the CSI feedback are welldefined, the determination of some of the CSI to be fed back is not soclearly defined. There exist two related issues to be addressed:

-   -   How is RI to be determined when PTI=1?    -   How is W2 to be determined when PTI=1?        The above issues arise from an absence of W1 or first PMI in the        second CSI report sequence.

According to an example embodiment, the CSI that are not clearlydefined, such as RI and/or W2 when PTI=1, may be determined conditionedon previously reported CSI. In other words, the UE may use previouslyreported CSI to help it generate the CSI that are not clearly defined.

FIG. 4 a illustrates a first diagram 400 of CSI feedback transmitted bya UE to an eNB, wherein one of the CSI is determined conditioned onpreviously reported CSI. First diagram 400 displays a number offeedbacks of CSI by a UE to a BS, including a RI with PTI=1 report(shown as subframe 405). However, as discussed previously, the UE maynot know how to determine the RI with PTI=1 report.

According to an example embodiment, the UE may be able to determine theRI with PTI=1 report conditioned on a previously reported first PMI orW1 report (shown as subframe 410) and a previously reported RI withPTI=0 report (shown as subframe 415). A detailed description of anexemplary determination of the RI with PTI=1 report from the previouslyreported first PMI or W1 report and the previously reported RI withPTI=0 report is provided below. Although it may be possible to utilizeany previously reported W1 or first PMI report and any previouslyreported RI with PTI=0 report to determine the RI with PTI=1 report aslong as the previously reported CSI belong to a different CSI reportsequence, the most recently reported (or similarly, last reported) W1 orfirst PMI report and the most recently reported (or similarly, lastreported) RI with PTI=0 report (as long as the previously reported CSIbelong to a different CSI report sequence) may produce the RI with PTI=1report that provides the best overall communications system performance.

As an illustrative example, consider codebook based precoding for closedloop MIMO communications system which may be expressed as

y=HPx+n,

where vector y represents the received signals, H represents the channelmatrix, P represents the precoding matrix or vector, x represents thevector consisting of signals to be transmitted, and n represents theobserved noise or interference at UE.

For a dual index or double codebook based codebook, such as the codebookfor eight transmit antenna in LTE Release-10, a precoding matrixrecommended by a UE is a matrix product expressible as

W _(i) ₁ _(,i) ₂ =W _(i) ₁ W _(i) ₂ .

For convenience, the precoding matrix or codewords in a rank r codebookmay be expressed as

W _(i) ₁ _(,i) ₂ ^((r)) =W _(i) ₁ ^((r)) W _(i) ₂ ^((r)).

Here rank=r, while i_(j) and i₂ are the first PMI and second PMI,respectively, and are used to index W_(i) ₁ ^((r)) and W_(i) ₂ ^((r)),also equivalently to jointly index matrix W_(i) ₁ _(,i) ₂ ^((r)).

The determination of the RI with PTI=1 report conditioned on the mostrecently reported RI with PTI=0 report and the most recently reported W1or first PMI report may be expressed as

${r_{1}^{*} = {\arg \underset{r_{1} \in R_{r_{0}^{*},i_{1}^{*}}^{(1)}}{\; \max}\left( {\max\limits_{i_{2}}{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)}} \right)}},$

where r₀* and i₁* are the most recently reported RI with PTI=0 reportand the most recently reported W1 or first PMI report, respectively, andR_(r) ₀ _(*) _(,i) ₁ _(*) ⁽¹⁾ represents a set of allowable r₁ valuessuch that W1 corresponding to first PMI i₁* in a rank −r₁ codebook issame as W1 corresponding to first PMI i₁* in a rank −r₀* codebook. Morespecifically, the candidate r₁ can be given in Table 1.

TABLE 1 Candidate RI with PTI = 1 reports conditioned on previouslyreported RI with PTI = 0 and a first PMI. r₀*, the last reported RI withPTI = 0 5, 6, 7 1, 2 3, 4 i₁* = 0 i₁* = 1, 2, 3 8 Candidate 1, 2 3, 4 5,6, 7, 8 5, 6, 7 5, 6, 7, 8 values of r₁

Therefore, given a value of r₀*, the UE may determine a set of candidatevalues for r₁ conditioned on the value of r₀* (using Table 1, forexample). In other words, the value of r r₀* is used to determine(condition) the set of candidate values for r₁. The UE may then select avalue from the set of candidate values as the RI with PTI=1 report. Forexample, the UE may make use of the channel measurement to select thevalue from the set of candidate values. As an illustrative example,consider a situation wherein r₀*=4, then the set of candidate values forr₁ comprises 3 and 4. The UE may then select either 3 or 4 for the RIwith PTI=1 report depending on the value of its channel measurement. Asanother illustrative example, consider a situation wherein r₀*=6 andi₁*=1, then the set of candidate values for r₁ comprises 5, 6 and 7. TheUE may then select either 5 or 6 or 7 for the RI with PTI=1 reportdepending on the channel measurement.

Furthermore,

${{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)} = {\sum\limits_{s \in S}^{\;}{C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, and s represents a subband belonging to S.

Alternatively, the determination of RI with PTI=1 report conditioned onthe most recently reported RI with PTI=0 and W1 or first PMI report canalso be expressed as

${r_{1}^{*} = {\arg \; {\max\limits_{r_{1} \in R_{r_{0}^{*},i_{1}^{*}}^{(1)}}\left( {\sum\limits_{s \in S}{\max\limits_{i_{2}}\left( {C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)} \right)}} \right)}}},$

where C_(s)(W_(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾) represents the totalthroughput, capacity, or other metrics when transmitting utilizingprecoding matrix W_(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾ on subband s and it canbe derived based on the following equation

y=HPx+n,P=W _(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾,

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example.

Furthermore, the rank indicator with PTI=1 can be further encoded intoat most a two bit representation. As an illustrative example, from Table1, if r₀*=1, 2, one bit can be used to encode r₁*: 0 for r₁*=1 and 1 forr₁*=2, or 0 for r₁*=2 and 1 for r₁*=1; while if r₀*=3,4 then, one bitcan be used to encode r₁*: 0 for r₁*=3 and 1 for r₁*=4, or 0 for r₁*=4and 1 for r₁*=3; while if r₀*=5, 6, 7, 8 then, two bits can be used toencode r₁*: 0, 1, 2, and 3 can be for r₁*=5, 6, 7, 8, respectively, andhere 0, 1, 2, and 3 can be represented by two bits.

According to an example embodiment, the UE may be able to determine theRI with PTI=1 report conditioned on a previously reported first PMI orW1 report and a previously reported RI with PTI=1 report. A detaileddescription of an exemplary determination of the RI with PTI=1 reportfrom the previously reported first PMI or W1 report and the previouslyreported RI with PTI=1 report is provided below. Although it may bepossible to utilize any previously reported W1 or first PMI report todetermine the RI with PTI=1 report, the most recently reported (orsimilarly, last reported) W1 or first PMI report may produce the RI withPTI=1 report that provides the best overall communications systemperformance.

As an illustrative example, consider codebook based precoding for closedloop MIMO communications system and a dual index or double codebookbased codebook. The determination of the RI with PTI=1 reportconditioned on the most recently reported (or similarly, last reported)W1 or first PMI report and the most recently reported (or similarly,last reported) RI with PTI=1 report and may be expressed as

${r_{1}^{*} = {\arg \; {\max\limits_{r_{1} \in R_{r_{1}^{\prime},i_{1}^{*}}^{(1)}}\left( {\max\limits_{i_{2}}{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)}} \right)}}},$

where r₁′ is the previously reported (e.g., most recently or lastreported) RI with PTI=1 report, i₁′ is the most recently reported orlast reported W1 or first PMI report, and R_(r) ₁ _(′) _(,i) ₁ _(*) ⁽¹⁾represents a set of allowable r₁ values such that W1 corresponding tofirst PMI i₁* in a rank −r₁ codebook is same as W1 corresponding tofirst PMI i₁* in a rank −r₁′ codebook. More specifically, the candidater₁ can be given in Table 2.

TABLE 2 Candidate RI with PTI = 1 reports conditioned on previouslyreported RI with PTI = 1 and a first PMI. r₁′, the last reported RI withPTI = 1 5, 6, 7 1, 2 3, 4 i₁* = 0 i₁* = 1, 2, 3 8 Candidate 1, 2 3, 4 5,6, 7, 8 5, 6, 7 5, 6, 7, 8 values of r₁

Therefore, for a given value of r₁′, the UE may determine a set ofcandidate values for r₁ conditioned on the value of r₁′ (using Table 2,for example). In other words, the value of r₁′ is used to determine(condition) the set of candidate values for r₁. The UE may then select avalue from the set of candidate values as the RI with PTI=1 report basedon the channel measurement. As an illustrative example, consider asituation wherein r₁′=2, then the set of candidate values for r₁comprises 1 and 2. The UE may then select either 1 or 2 for the RI withPTI=1 report depending on its channel measurement. As anotherillustrative example, consider a situation wherein r₁′=5 and i₁*=0, thenthe set of candidate values for r₁ comprises 5, 6, 7 and 8. The UE maythen select either 5, 6, 7 or 8 for the RI with PTI=1 report dependingon its channel measurement.

Furthermore,

${{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)} = {\sum\limits_{s \in S}{C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, and s represents a subband belonging to S.

Alternatively, the determination of RI with PTI=1 report conditioned onthe previously reported (e.g., most recently reported or last reported)RI with PTI=1 report and the previously reported (e.g., most recentlyreported or last reported) W1 or first PMI report can also be expressedas

${r_{1}^{*} = {\arg \; {\max\limits_{r_{1} \in R_{r_{1}^{\prime},i_{1}^{*}}^{(1)}}\left( {\sum\limits_{s \in S}{\max\limits_{i_{2}}\left( {C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1})} \right)} \right)}} \right)}}},$

where C_(s)(W_(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾) represents the totalthroughput, capacity, or other metrics when transmitting utilizingprecoding matrix W_(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾ on subband s and it canbe derived based on the following equation

y=HPx+n,P=W _(i) ₁ _(*) _(,i) ₂ ^((r) ¹ ⁾,

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example.

Furthermore, the rank indicator with PTI=1 can be further encoded intoat most a two bit representation. As an illustrative example, from Table1, if r₁′=1, 2, then one bit can be used to encode if r₁*: 0 for r₁*=1and 1 for r₁*=2, or 0 for r₁*=2 and 1 for if =1; while if r₁′=3, 4 then,one bit can be used to encode r₁*: 0 for r₁*=3 and 1 for r₁*=4, or 0 forr₁*=4 and 1 for r₁*=3; while if r₁′=5, 6, 7, 8; two bits can be used toencode r₁*: 0, 1, 2, and 3 can be for r₁*=5, 6, 7, 8, respectively, andhere 0, 1, 2, and 3 can be represented by two bits.

FIG. 4 b illustrates a second diagram 430 of CSI feedback transmitted bya UE to an eNB, wherein one of the CSI is determined conditioned onpreviously reported CSI. Second diagram 430 displays a number offeedbacks of CSI by a UE to an eNB, including a wideband W2 or widebandsecond PMI report (shown as subframe 435). However, as discussedpreviously, the UE may not know how to determine the wideband second PMIor W2 report when PTI is set to 1.

According to an example embodiment, the UE may be able to determine thewideband W2 or wideband second PMI report conditioned on a RI with PTI=1report (shown as subframe 440) and a W1 or first PMI report (shown assubframe 445). A detailed description of an exemplary determination ofthe wideband W2 or wideband second PMI report is provided below.Although it may be possible to utilize any previously reported RI withPTI=1 report and any previously reported W1 or first PMI report todetermine the wideband second PMI or W2 report as long as there exists apreviously reported W1 or first PMI report, which belongs to a differentCSI report sequence, the most recently reported (or similarly, lastreported) RI with PTI=1 report and the most recently reported (orsimilarly, last reported) W1 or first PMI report (as long as thereexists a previously reported W1 or first PMI report, which belongs to adifferent CSI report sequence) may produce the wideband W2 or widebandsecond PMI report that provides the best overall communications systemperformance. It is noted that the RI with PTI=1 report may be determinedconditioned on previously reported CSI such as described in thedescription of FIG. 4 a.

As an illustrative example, considering the above mentioned MIMO systemand dual index or double codebook based codebook, the determination ofthe wideband W2 or wideband second PMI report conditioned on the mostrecently reported (or similarly, last reported) RI with PTI=1 report andthe most recently reported (or similarly, last reported) first PMI or W1report may be expressed as

${i_{2}^{*} = {\arg \; {\max\limits_{i_{2}}{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1}^{*})} \right)}}}},$

where r₁* and i₁* is the most recently reported (or similarly, lastreported) RI with PTI=1 report and the most recently reported (orsimilarly, last reported) wideband first PMI or W1 report, respectively.

Furthermore,

${{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{1}^{*})} \right)} = {\sum\limits_{s \in S}{C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1}^{*})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, s represents a subband belonging to S, and

C_(s)(W_(i₁^(*), i₂)^((r₁^(*))))

represents the total throughput, capacity, or other metrics whentransmitting utilizes precoding matrix

W_(i₁^(*), i₂)^((r₁^(*)))

on subband s and it can be derived based on

y = HPx + n, P = W_(i₁^(*), i₂)^((r₁^(*))),

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example. Furthermore, a wideband CQI canbe calculated conditioned on the precoding matrix

W_(i₁^(*), i_(2^(*)))^((r₁^(*)))

assuming transmission occurs over set S subbands or the entire systembandwidth.

FIG. 4 c illustrates a third diagram 460 of CSI feedback transmitted bya UE to an eNB, wherein one of the CSI is determined conditioned onpreviously reported CSI. Third diagram 460 displays a number offeedbacks of CSI by a UE to an eNB, including a subband W2 or second PMIreport (shown as subframe 465). However, as discussed previously, the UEmay not know how to determine the subband second PMI or W2 report whenPTI is set to 1.

According to an example embodiment, the UE may be able to determine thesubband W2 or second PMI report conditioned on a RI with PTI=1 report(shown as subframe 470) and a W1 or first PMI report (shown as subframe475). A detailed description of an exemplary determination of thesubband W2 or second PMI report is provided below. Although it may bepossible to utilize any previously reported RI with PTI=1 report and anypreviously reported W1 or first PMI report to determine the subband W2or second PMI report as long as there exists a previously reported W1 orfirst PMI report that belongs to a different CSI report sequence, themost recently reported (or similarly, last reported) RI with PTI=1report and the most recently reported (or similarly, last reported)first PMI or W1 report (as long as there exists a previously reported W1or first PMI report, which belongs to a different CSI report sequence)may produce the subband W2 or second PMI report that provides the bestoverall communications system performance. It is noted that the RI withPTI=1 report may be determined conditioned on previously reported CSIsuch as described in the description of FIG. 4 a.

As an illustrative example, considering the above mentioned MIMO systemand dual index or double codebook based codebook, the determination ofthe subband W2 or second PMI report conditioned on the most recentlyreported (or similarly, last reported) RI with PTI=1 report and the mostrecently reported (or similarly, last reported) W1 or first PMI reportmay be expressed as

${i_{2}^{*} = {\arg \; {\max\limits_{i_{2}}{C_{s^{*}}\left( W_{i_{1}^{*},i_{2}}^{(r_{1}^{*})} \right)}}}},$

where r₁* and i₁* are the most recently reported (or similarly, lastreported) RI with PTI=1 report and the most recently reported (orsimilarly, last reported) wideband W1 or first PMI report, respectively,and s* represents the subband selected by UE. It is noted that a subbandselection indicator or a subband label in a BP can be reported withsubband second PMI report for this situation. The subband selected froma BP can be expressed by

${s^{*} = {\arg \; {\max\limits_{s}\left( {\max\limits_{i_{2}}{C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{1}^{*})} \right)}} \right)}}},$

where s belongs to a particular BP or determined by predefined cycling(for this situation, the subband selection indicator or the subbandlabel may be used by a predefined cycling pattern known by the UE andthe eNB and may not necessarily be reported. For example, the subbandlabel may be used in increasing order of frequency per BP. Furthermore,

C_(s^(*))(W_(i₁^(*), i₂)^((r₁^(*))))

represents the total throughput, capacity, or other metrics whentransmitting utilizes precoding matrix

W_(i₁^(*), i₂)^((r₁^(*)))

on subband s* and it can be derived based on

y = HPx + n, P = W_(i₁^(*), i₂)^((r₁^(*))),

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example. Furthermore, a subband CQI can becalculated conditioned on the precoding matrix

W_(i₁^(*), i₂^(*))^((r₁^(*)))

assuming transmission over subband s*.

According to an example embodiment, the UE may determine a PTI. Adetailed description of an exemplary determination of the PTI isprovided below. The PTI can be set to 0 and reported with RI for thefirst feedback, as an example. Then several PTI=0 or PTI=1 can be fedback at different instances based on a RI report period, which can beaccording to a predefined cycling pattern (for example, five reportinstances of PTI=1 per one report instance of PTI=0 or two reportinstances of PTI=0 followed by one report instance of PTI=1), channelconditions or traffic type, or so on. Furthermore, PTI can be alsoreported at a different subframe from the RI report, for example, PTIcan be reported with the same period but with an offset with respect tothe RI report.

According to an example embodiment, the UE may determine a RI when PTI=0report. A detailed description of an exemplary determination of the RIwith PTI=0 report is provided below.

As an illustrative example, consider codebook based precoding for closedloop MIMO communications system and a dual index or double codebookbased codebook. The determination of the RI with PTI=0 report may beexpressed as

${r_{0}^{*} = {\arg \; {\max\limits_{r_{0}}\left( {\max\limits_{i_{1},i_{2}}{f_{WB}\left( W_{i_{1},i_{2}}^{(r_{0})} \right)}} \right)}}},{and}$${{f_{WB}\left( W_{i_{1},i_{2}}^{(r_{0})} \right)} = {\sum\limits_{s \in S}{C_{s}\left( W_{i_{1},i_{2}}^{(r_{0})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, and s represents a subband belonging to S.

Alternatively, the determination of RI when with PTI=0 can also beexpressed as

${r_{0}^{*} = {\arg \; {\max\limits_{r_{0}}\left( {\max\limits_{i_{1}}{\sum\limits_{s \in S}{\underset{i_{2}}{\max \;}\left( {C_{s}\left( W_{i_{1},i_{2}}^{(r_{0})} \right)} \right)}}} \right)}}},$

where C_(s)(W_(i) ₁ _(,i) ₂ ^((r) ⁰ ⁾) represents the total throughput,capacity, or other metrics when transmitting utilizing precoding matrixW_(i) ₁ _(,i) ₂ ^((r) ⁰ ⁾ on subband s and it can be derived based onthe following equation

y=HPx+n,P=W _(i) ₁ _(,i) ₂ ^((r) ⁰ ⁾,

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example.

According to an example embodiment, the UE may determine a wideband W1or wideband first PMI report conditioned on a previously reported (e.g.,most recently reported or the last reported) RI with PTI=0 report. Adetailed description of an exemplary determination of the wideband W1 orwideband first PMI report is provided below.

As an illustrative example, considering the above mentioned MIMO systemand dual index or double codebook based codebook, the determination ofthe wideband W1 or wideband first PMI report conditioned on the lastreported (or similarly, most recently reported) RI with PTI=0 report maybe expressed as

${i_{1}^{*} = {\arg \; {\max\limits_{i_{1}}\left( {\max\limits_{i_{2}}{f_{WB}\left( W_{i_{1},i_{2}}^{(r_{0}^{*})} \right)}} \right)}}},$

where r₀* is the most recently reported or the last reported RI withPTI=0.

Furthermore,

${{f_{WB}\left( W_{i_{1},i_{2}}^{(r_{0}^{*})} \right)} = {\sum\limits_{s \in S}{C_{s}\left( W_{i_{1},i_{2}}^{(r_{0}^{*})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, s represents a subband belonging to S.

Alternatively, the determination of the wideband W1 or wideband firstPMI report conditioned on the last reported RI with PTI=0 report may beexpressed as

${i_{1}^{*} = {\arg \; {\max\limits_{i_{1}}\left( {\sum\limits_{s \in S}{\max\limits_{i_{2}}{C_{s}\left( W_{i_{1},i_{2}}^{(r_{0}^{*})} \right)}}} \right)}}},$

where

C_(s)(W_(i₁, i₂)^((r₀^(*))))

represents the total throughput, capacity, or other metrics whentransmitting utilizing precoding matrix

W_(i₁, i₂)^((r₀^(*)))

on subband s and it can be derived based on

y = HPx + n, P = W_(i₁, i₂)^((r₀^(*))),

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example.

According to an example embodiment, the UE may determine a wideband W2or wideband second PMI report conditioned on previously reported (e.g.,most recently reported or the last reported) RI with PTI=0 report andpreviously reported (e.g., most recently reported or the last reported)wideband first PMI report when PTI=0. A detailed description of anexemplary determination of the wideband W2 or wideband second PMI reportis provided below.

As an illustrative example, considering the above mentioned MIMO systemand dual index or double codebook based codebook, the determination ofthe wideband W2 or wideband second PMI report conditioned on the lastreported or most recently reported RI with PTI=0 report and the widebandW1 or the first PMI report when PTI=0 may be expressed as

${i_{2}^{*} = {\arg \; {\max\limits_{i_{2}}{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{0}^{*})} \right)}}}},$

where r₀* and i₁* are the most recently reported or the last reported RIand wideband first PMI when PTI is set to 0.

Furthermore,

${{f_{WB}\left( W_{i_{1}^{*},i_{2}}^{(r_{0}^{*})} \right)} = {\sum\limits_{s \in S}{C_{s}\left( W_{i_{1}^{*},i_{2}}^{(r_{0}^{*})} \right)}}},$

where S represents the set of subbands and spans the entire systembandwidth, s represents a subband belonging to S.

C_(s)(W_(i₁^(*), i₂)^((r₀^(*))))

represents the total throughput, capacity, or other metrics whentransmitting utilizing precoding matrix

W_(i₁^(*), i₂)^((r₀^(*)))

on subband s and it can be derived based on

y = HPx + n, P = W_(i₁^(*), i₂)^((r₀^(*))),

by utilizing MIMO capacity formula or other metric such as mutualinformation based metric, for example. Furthermore, a wideband CQI canbe calculated conditioned on the precoding matrix

W_(i₁^(*), i₂^(*))^((r₀^(*)))

assuming transmission occurs over set S subbands or the entire systembandwidth.

According to an example embodiment, the eNB may receive PTI and/or RIreports. Specifically, PTI and/or RI reports can be received at apredefined subframe. For example, the subframe may be at a multiple of aperiod for CQI or PMI reports with specified offset, which can beconfigured by higher layer signaling.

According to an example embodiment, the eNB may receive a wideband firstPMI report based on a most recently received PTI report. Specifically,based on the most recently received PTI=0 report, eNB may receive thewideband first PMI report at a particular subframe, which can beconfigured by higher layer signaling and may be different for differentvalues of PTI.

According to an example embodiment, the eNB may receive a widebandsecond PMI report conditioned on the most recently received PTI.Specifically, based on the most recently received PTI=0 or PTI=1 report,eNB may receive the wideband second PMI report at a particular subframe,which can be configured by higher layer signaling and may be differentfor different values of PTI. Furthermore, a wideband CQI report can bealso received together with the wideband second PMI report.

According to an example embodiment, the eNB may receive a subband secondPMI report conditioned on the most recently received PTI. Specifically,based on the most recently received PTI=1 report, eNB may receive thesubband second PMI report at a particular subframe, which can beconfigured by higher layer signaling; Furthermore, a subband CQI reportcan be also received together with the wideband second PMI report.

According to an example embodiment, the eNB may obtain a precodingmatrix based the most recently received PTI and CSI reports. A detaileddescription of an exemplary reception of PTI and/or RI reports isprovided below. If the most recently received PTI report comprises aPTI=0 report, then the precoding matrix can be

W_(i₁^(*), i₂^(*))^((r₀^(*)))

where r₀*, i₁* and i₂* are most recently RI, first PMI, and second PMIwhen PTI=0, respectively. If the most recently received PTI reportcomprises a PTI=1 report, then the precoding matrix can be

W_(i₁^(*), i₂^(*))^((r^(*)))

where i₂* is the most recently or last received (wideband or subband)second PMI report when PTI=1, i₁* is the most recently or last receivedfirst PMI when PTI=0, and r* is the most recently RI when PTI=0 or PTI=1that is consistent with assumptions at UE regarding the value of PTI.

FIG. 5 illustrates a flow diagram of UE operations 500 in reporting CSIto an eNB. UE operations 500 may be indicative of operations occurringin a UE, such as UE 110 or UE 203, as the UE reports CSI to an eNB, suchas eNB 105 or eNB 201. UE operations 500 may occur while the UE is in anormal operating mode.

UE operations 500 may begin with the UE estimating a channel betweenitself and the eNB (block 505). According to an example embodiment, theUE may estimate the channel based on signals transmitted by the eNB. Asan example, the UE may estimate the channel based on a pilot signal, areference signal such as cell specific reference signal (CRS) or channelstate information reference signal (CSI-RS), a preamble, or so on,transmitted by the eNB.

The UE may determine the CSI to be reported to the eNB (block 510) basedon the channel estimate or channel measurement. According to an exampleembodiment, how the UE determines the CSI to be reported to the eNBdepends upon the type of CSI reported to the eNB, e.g., PTI=0 or PTI=1.As an example, certain CSI may be determinable by the UE without beingconditioned on the previously reported CSI associated with a differenttype of CSI, while other CSI may require the UE to determine the CSIconditioned on the previously reported CSI associated with a differenttype of CSI.

The UE may determine the type of CSI, where the CSI is to be reported tothe eNB (block 515). As an illustrative example, in order to supportclosed loop MIMO, the types of CSI by the UE may include PTI=1, PTI=0,and so on.

With the type of CSI determined, the UE may perform a check to determineif the CSI requires knowledge of previously reported CSI, which may ormay not be associated with a different type of CSI (block 520). If theCSI does not require knowledge of previously reported CSI associatedwith a different type of CSI, the UE may determine the CSI from themeasurements of the channel (block 525).

However, if the CSI does require knowledge of previously reported CSI,the UE may obtain the previously reported CSI dependent on the type ofCSI (block 530). As illustrative examples, CSI that does requireknowledge of previously reported CSI associated with a different type ofCSI include RI report with PTI=1, wideband W2 or second PMI report withPTI=1, subband W2 or second PMI report with PTI=1, and so forth.

The UE may determine the CSI conditioned on the previously reported CSIand potentially the type of CSI (block 535). As illustrative examples,the UE may determine the RI with PTI=1 report conditioned on the mostrecently (or last) reported wideband W1 or first PMI report and the mostrecently reported (or last reported) RI with PTI=0 report (as shown inblocks 605 in FIG. 6 a); the wideband W2 or second PMI reportconditioned on the most recently reported (or last reported) RI withPTI=1 report and the most recently reported (or last reported) widebandW1 or first PMI report (as shown in block 610 in FIG. 6 b); the subbandW2 or second PMI report conditioned on the most recently reported (orlast reported) RI with PTI=1 report and the most recently reported (orlast reported) wideband W1 or first PMI report (as shown in block 615 inFIG. 6 c); and so on.

According to an example embodiment, depending on the CSI, the previouslyreported CSI that the UE uses to condition its determination of the CSIis associated with a CSI report sequence different from a CSI reportsequence that is associated with the CSI that it is determining. As anillustrative example, the UE may determine the RI with PTI=1 reportbelonging to the second CSI report sequence conditioned on the mostrecently reported (or last reported) wideband W1 or first PMI report andthe most recently reported (or last reported) RI with PTI=0 reportassociated with the first CSI report sequence.

The UE may report the CSI to the eNB (block 540). Alternatively, the UEmay report the type of CSI or both the CSI and the type of CSI to theeNB.

FIG. 7 provides an illustration of a communications device 700.Communications device 700 may be an implementation of a UE, MS, or soon. Communications device 700 may be used to implement various ones ofthe embodiments discussed herein. As shown in FIG. 7, a transmitter 705is configured to transmit information and a receiver 710 is configuredto receive information. Transmitter 705 and receiver 710 may have awireless interface, a wireline interface, or a combination thereof. Inpractice, transmitter 705 and receiver 710 might be implemented in asingle unit of hardware.

A channel estimation unit 720 is configured to measure a channel betweencommunications device 700 and an eNB (or a BS or any other form ofcommunications controller). Channel estimation unit 720 makes use ofsignals, such as pilot signals, reference signals, preambles, and so on,transmitted by the eNB to measure the channel. A memory accessing unit722 is configured to retrieve previously reported channel informationfrom a memory 740 in order to determine certain types of channelinformation to report to the eNB. The previously reported channelinformation may be organized in a reported channel information store742, for example.

A channel information processing unit 724 is configured to determine CSIto report to the eNB. Depending on the type of the CSI being reported,channel information processing unit 724 may make use of channelmeasurements, previously reported channel information, CSI type, or acombination thereof to determine CSI. A feedback generating unit 726 isconfigured to generate feedback information from CSI. For example,feedback generating unit 626 may generate coded bit sequence andmodulation symbol sequence from CSI.

A codebook unit 730 is configured to maintain a codebook to meetoperating conditions. A memory 740 is configured to store reportedchannel information, channel measurements, and so forth.

The elements of communications device 700 may be implemented as specifichardware logic blocks. In an alternative, the elements of communicationsdevice 700 may be implemented as software executing in a processor,microprocessor, digital signal processor, controller, applicationspecific integrated circuit, or so on. In yet another alternative, theelements of communications device 700 may be implemented as acombination of software and/or hardware.

As an example, transmitter 705 and receiver 710 may be implemented as aspecific hardware block, while channel estimation unit 720, memoryaccessing unit 722, channel information processing unit 724, feedbackgenerating unit 726, and codebook unit 730 may be software modulesexecuting in a processor 715, such as a microprocessor, a digital signalprocessor, a custom circuit, or a custom compiled logic array of a fieldprogrammable logic array.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method for reporting channel information, the method comprising: determining, at a user equipment, a channel information type for first channel information to be reported to a communications controller; determining the first channel information conditioned on previously reported channel information and on the channel information type; and reporting the first channel information, the channel information type, or a combination thereof, to the communications controller.
 2. The method of claim 1, wherein the previously reported channel information is obtained based on the channel information type.
 3. The method of claim 1, wherein the first channel information comprises channel state information.
 4. The method of claim 1, wherein the determining the first channel information comprises: selecting a candidate channel information set based on the previously reported channel information; and selecting the first channel information from the candidate channel information set.
 5. The method of claim 1, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the determining the first channel information comprises determining a rank indicator with the indicator set to the first value conditioned on the previously reported channel information.
 6. The method of claim 5, wherein the previously reported rank indicator comprises a last reported rank indicator, and wherein the previously reported wideband first precoding matrix indicator comprises a last reported wideband first precoding matrix indicator.
 7. The method of claim 5, wherein the indicator comprises a precoding type indicator and the first value is equal to 1, and wherein the determining the rank indicator with the indicator set to the first value comprises: selecting a set of candidate rank indicators from a plurality of sets of candidate rank indicators based on the previously reported rank indicator and the previously reported wideband first precoding matrix indicator; and selecting a candidate rank indicator from the set of candidate rank indicators as the rank indicator with the indicator set to the first value, wherein the plurality of sets of candidate rank indicators are as shown, previously reported rank indicator with precoding type indicator = 0 or 1 5, 6, 7 1, 2 3, 4 i1 = 0 i1 = 1, 2, 3 8 Set of 1, 2 3, 4 5, 6, 7, 8 5, 6, 7 5, 6, 7, 8 candidate rank indicators with precoding type indicator = 1

where i1 is the previously reported wideband first precoding matrix indicator.
 8. The method of claim 7, wherein the determining the rank indicator with the indicator set to the first value further comprises encoding the rank indicator with the indicator set to the first value into at most two bit representation.
 9. The method of claim 5, wherein the previously reported wideband first precoding matrix indicator is obtained conditioned on the indicator set to a second value.
 10. The method of claim 1, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the determining the first channel information comprises determining a wideband second precoding matrix indicator conditioned on the previously reported channel information.
 11. The method of claim 10, wherein the previously reported rank indicator comprises a last reported rank indicator, and wherein the previously reported wideband first precoding matrix indicator comprises a last reported wideband first precoding matrix indicator.
 12. The method of claim 1, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the determining the first channel information comprises determining a subband second precoding matrix indicator conditioned on the previously reported channel information.
 13. The method of claim 12, wherein the previously reported rank indicator comprises a last reported rank indicator, and wherein the previously reported wideband first precoding matrix indicator comprises a last reported wideband first precoding matrix indicator.
 14. A user equipment comprising: a processor configured to determine a channel information type for first channel information to be reported to a communications controller, and to determine the first channel information conditioned on previously reported channel information and on the channel information type; and a transmitter coupled to the processor, the transmitter configured to report the first channel information, the channel information type, or a combination thereof, to the communications controller.
 15. The user equipment of claim 14, wherein the processor is configured to obtain the previously reported channel information based on the channel information type.
 16. The user equipment of claim 14, wherein the processor is configured to determine the first channel information by selecting a candidate channel information set based on the previously reported channel information, and selecting the first channel information from the candidate channel information set.
 17. The user equipment of claim 14, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a rank indicator with the indicator set to the first value conditioned on the previously reported channel information as the first channel information.
 18. The user equipment of claim 17, wherein the wideband first precoding matrix indicator is obtained conditioned on the indicator set to a second value.
 19. The user equipment of claim 14, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a wideband second precoding matrix indicator conditioned on the previously reported channel information as the first channel information.
 20. The user equipment of claim 14, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a subband second precoding matrix indicator conditioned on the previously reported channel information as the first channel information.
 21. The user equipment of claim 14, wherein the previously reported channel information comprises a last reported channel information.
 22. A communications system comprising: a communications controller configured to control user equipment; and a user equipment coupled to the communications controller, the user equipment configured to determine a channel information type for first channel information to be reported to the communications controller, to determine the first channel information conditioned on previously reported channel information and on the channel information type, and to report the first channel information, the channel information type, or a combination thereof, to the communications controller.
 23. The communications controller of claim 22, wherein the user equipment is configured to obtain the previously reported channel information based on the channel information type.
 24. The communications controller of claim 22, wherein the user equipment comprises: a processor configured to determine the channel information type, and to determine the first channel information conditioned on the previously reported channel information; and a transmitter configured to report the first channel information, or the channel information type, or a combination thereof, to the communications controller.
 25. The communications controller of claim 24, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a rank indicator with the indicator set to the first value conditioned on the previously reported channel information as the first channel information.
 26. The communications controller of claim 25, wherein the wideband first precoding matrix indicator is obtained conditioned on the indicator set to a second value.
 27. The communications controller of claim 24, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a wideband second precoding matrix indicator conditioned on the previously reported channel information as the first channel information.
 28. The communications controller of claim 24, wherein the channel information type comprises an indicator set to a first value, and wherein the previously reported channel information comprises a previously reported rank indicator and a previously reported wideband first precoding matrix indicator, and wherein the processor determines a subband second precoding matrix indicator conditioned on the previously reported channel information as the first channel information.
 29. The communications controller of claim 22, wherein the previously reported channel information comprises a last reported channel information. 